Ref: http://physicsweb.org/articles/news/8/12/11/1
Supercool helium ions make their debut
20 December 2004
Physicists in Germany have produced large numbers of ultracold helium
ions for the first time. The helium ions could be used to search for
variations in the values of the fundamental constants and to test
various effects in quantum electrodynamics (QED).
Established laser cooling techniques do not work for helium so
Stephan Schiller and colleagues at Heinrich-Heine University in
Düsseldorf had to use a technique called "sympathetic cooling"
instead. This involved cooling the ions with a gas of beryllium ions
that had already been cooled with lasers (B Roth et al. 2004
http://arXiv.org/abs/physics/0412053 ).
See: http://physicsweb.org/articles/news/8/12/11/1
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